Access to multimedia content, such as television, from a network of Internet type, is possible today. Television over the Internet allows a user of a terminal, connected to a television content channels server via a telecommunication network, to render, or play back, a digital channel of his choice from among a predetermined list of possible channels.
The terminal generally emits a request destined for a server, indicating the chosen channel and it receives in return a stream of digital data relating to this channel.
A digital channel typically comprises films, videos, or in a more general manner any type of digital content which can be transmitted in the network considered.
The terminal is adapted for receiving these digital contents in the form of multimedia data and for effecting playback thereof. This playback consists in providing at the level of the terminal the digital content in a form accessible to the user. For example, data received corresponding to a video are generally decoded, and then played back at the level of the terminal in the form of a display, or viewing, of the corresponding video with its associated sound track. Hereinafter, the digital content will be regarded as a video and the playback by the terminal, or consumption by the user of the terminal, as a viewing on the screen of the terminal.
The broadcasting of channels of digital contents over the Internet is often based on client-server protocols of the HTTP (standing for Hyper Text Transport Protocol) family. In particular, the downloading in progressive mode of the digital contents, also called streaming, makes it possible to transport and consume the data in real time, that is to say the digital data are transmitted over the network and played back by the terminal as and when they arrive. The terminal typically receives part of the digital data in a buffer memory before playing them back. This mode of distribution is particularly useful when the bitrate at the user's disposal is not guaranteed for the real-time transfer of video.
Adaptive progressive downloading, known as HTTP Adaptative Streaming (HAS for short), makes it possible moreover to broadcast and receive data according to various qualities corresponding for example to various bitrates. These various qualities are described in a parameter file available by downloading on a data server, for example a contents channels server. When the client terminal desires to access a channel of contents, this description file makes it possible to select the appropriate format for the content to be consumed as a function of the bandwidth available, the client terminal's storage and decoding capabilities or else the size of its screen. This type of technique makes it possible in particular to take account of the variations in bandwidth on the link between the client terminal and the contents channels server.
Several technical solutions exist for facilitating the distribution of such a content by streaming, such as for example the proprietary solutions Microsoft Smooth Streaming, Apple HLS, Adobe Http Dynamic Streaming or else the ISO/IEC organization's MPEG-DASH standard which will be described hereinafter. These schemes propose to address to the client one or more intermediate description files, also called documents or digests, containing the addresses of the various segments with the various qualities of the multimedia content.
If a second progressive downloading is launched in parallel with a first, for example by the same terminal, or by another terminal of the same local network, the total bandwidth available for downloading is divided in equal shares between the two downloaded streams. Likewise, the simultaneous downloading of more than two streams will require a division in equal shares in such a way that the same bandwidth is at the disposal of each stream. Indeed, the HTTP protocol is based on principles of equality of access to a resource. The HTTP protocol is in particular based on protocols of TCP-IP type (set of protocols used for the transfer of the data over the Internet) which makes it possible to convey the packets of data between the various terminals and servers and the service gateway. The service gateway which receives the packets of data transported according to TCP-IP does not assign them any priority, thus culminating in an equal sharing of the bandwidth. In particular, if two downloads are launched in parallel by the same terminal, the same algorithm for selecting the quality of the content as a function of the bandwidth available is used, culminating in a sharing in two equal parts of the bandwidth available.
However, several downloaded video data streams intended to be played back on one and the same screen do not necessarily require, from a point of view of the user, the same bitrate. For example, certain video inlaying techniques (known as PIP, standing for PictureInPicture) generally make it possible to display in a small window a second video on the screen. It is desirable, in this context, that the user can assign a bigger bitrate to the main video, to the detriment of the inlaid video. The problem extends to a greater number of videos displayed simultaneously on the screen or on several playback devices of the local network.
According to certain implementations, it is known to adapt the capture of the content to certain parameters chosen by the user: for example, a given channel is encoded, decoded, and therefore played back in a variable quality depending on certain parameters chosen by the user. For example, patent US2007/0024705 (Systems and methods for video stream selection) describes such a mechanism in the context of a mosaic of contents for which the encoding bitrate for a given content is rendered proportional to the size occupied by the window for playback of the content in the mosaic.
In this type of implementation, however, it is the capture of the video which is conditioned by the size of the window in the mosaic. A modification of the size of this window may be followed by a fairly long time for modifying the bitrate of the content to be transported. Moreover, it imposes a modification of the physical conditions of acquisition (capture and compression of video, audio, etc.) of the digital content at the source.
There does not exist, to date, any solution for intelligently sharing the bitrate between several streams downloaded progressively in an adaptive manner (HAS) and played back on terminals of the local network with different playback characteristics, without imposing a modification of the acquisition of the content.